The dura mater is the tough outermost layer of fibrous tissue that encapsulates the brain and spinal cord. It serves to protect and isolate the neural tissue and it serves as a watertight membrane that contains the cerebrospinal fluid (CSF). Repair or reconstruction of the dura mater may be necessary as a result of trauma or neurosurgical procedures requiring an incision or removal of a segment of the dura mater. Many different materials have been used to reconstruct the dura mater including various tissues from the patient's body or from animals and various synthetic materials. Various biological substances that have been tried include collagen sponges and membranes, fibrin film, and processed dermis.
Synthetic sheet materials used clinically include metal foils, natural rubber, silicone rubber, urethane, polyester and polyethylene. None of these has proven ideal for long term clinical success.
The ideal dura substitute should be nontoxic, biocompatible, non-immunogenic, free from foreign body reaction, free from the risk of disease transmission, watertight, able to self-seal, conformable, flexible, non-adherent, easy to use, and readily available. Only a few devices have come close to providing all of these attributes. Glutaraldehyde fixed bovine pericardium (such as materials sold under the DURA GUARD® trademark by BioVascular, Inc.) has been prepared commercially and meets many of the criteria. Although bovine pericardium has generally been used successfully, it can create adhesions, elicit an immunologic reaction and may expose patients to a possibility of disease transmission. Expanded polytetrafluoroethylene (such as material sold under the PRECLUDE® trademark by W. L. Gore & Associates, Inc.) has also been used quite successfully with the advantages being an absence of adhesions and having no risk of disease transmission. Although these materials have met with clinical success, they require suturing to the adjacent tissue to obtain a liquid tight closure. Suturing can take up to 30 minutes or more.
In recent years it has become known that some neurosurgical procedures do not require an immediate liquid tight closure and surgeons have shown some degree of success using porous collagen sponges in some applications (such as with material sold under the DURAGEN® trademark by Integra NeuroCare). Particularly near the top of the skull, the CSF pressure is relatively low so leakage is not as likely as would be the case at the base of the skull or in the spine where the pressure is higher. In areas of higher pressure, it is important to obtain an immediate liquid tight closure so that patients do not suffer from headaches and the possibility of infections secondary to CSF leakage. In light of these recent changes in neurosurgical practice, another ideal attribute of a dura substitute is the capability of being used with or without sutures depending on the requirements of the surgical procedure.
In addition to the requirements listed above for any dura substitute, there are several requirements for a material to be acceptable for use as a dura substitute that can be used with or without sutures. To be appropriate for use in sutured applications, the material itself should be liquid tight and have requisite strength to hold sutures to enable its use in high pressure applications. This eliminates collagen sponges since they are not liquid tight and they have no structural integrity once wetted. Also, a sutured membrane should be able to “seal” at the points where sutures penetrate the material. To facilitate the creation of a wrinkle- or pucker-free suture line, the ideal sutured material should be flexible, elastic, and resilient. For the material to also be used in sutureless applications, it should have the capability of being selectively incorporated with adjacent tissue, while preventing ingrowth or adhesion to neural tissue such as the brain or spinal cord.
A material such as PRECLUDE® Dura Substitute meets many of the requirements for a dura substitute but it is not suitable for use in sutureless applications because it does not allow for the tissue ingrowth or incorporation that will prevent migration. It also has limited elasticity, and therefore it is not easily conformed when sutured in place.
An improved material would have many of the attributes of PRECLUDE® Dura Substitute while allowing tissue ingrowth on the side facing away from the neural tissue as well as having greater elasticity. Used without sutures, the material would be tucked under the edges of the native dura with the tissue ingrowth surface facing away from the neural tissue. Implantation would be similar in both dura reconstruction procedures or flap closure procedures. When used in sutured applications, the material would be oriented in the same way but sutured to the edges of the native dura.